Rios was born in The South Bronx in New York City to parents of Puerto Rican descent. He grew up in the Soundview neighborhood and had at least two sisters and one brother.^[6][7][2] He regularly played basketball and trained in boxing.^[6]

He moved out of his mother's house at age 15 and was homeless for a period of time in the late 1980s.^[8] Later, he received a large settlement from the city stemming from an incident in 1976, where Rios broke his leg while playing in a park.^[9]Using his settlement money, Rios married his high school sweetheart, Liza, and the two moved into a home together.

Rios struggled with depression stemming from his turbulent childhood, and he coped with it by overeating. Between the ages of 18 and 21, Rios' weight rocketed from 180 lb (82 kg) to 300 lb (140 kg); he was subsequently unable to tie his own shoes.^[8][6]

During the late 1980s, he began writing rap lyrics. He later formed the underground group Full-A-Clips with Lyrical Assassin, Joker Jamz, and Toom. Rios made a number of recordings with the group in the 1990s, which have not been released. At this point, Rios was operating under the alias Big Moon Dawg.^[10] After changing his stage name to Big Punisher, Rios met fellow Puerto Rican and Bronx rapper Fat Joe in 1995 and made his commercial debut on Fat Joe's second album, Jealous One's Envy, in addition to appearing on the song, "Watch Out". He also appeared in The Beatnuts' song "Off the Books".

In 1997, Big Pun began recording songs for his debut album Capital Punishment. In 1997, producer Knobody's production partner Sean C took advantage of his new role as A&R at Loud Records to play Knobody's tracks to Big Pun.^[11]Suitably impressed, the rapper hired Knobody to remix "I'm Not a Player".^[11] The remixed song, featuring Joe and titled "Still Not a Player", became Big Pun's first major mainstream hit and major breakthrough for Knobody.^[11] The full-length debut Capital Punishment followed in 1998, and became the first album by a solo Hispanic rapper to go platinum,^[5] peaking at No. 5 on the Billboard 200. Capital Punishment was also nominated for the Grammy Award for Best Rap Album.

Big Pun became a member of Terror Squad, a New York–based group of rappers founded by Fat Joe, with most of the roster supplied by the now-defunct Full-A-Clips who released their debut album The Album in 1999. The album did not fare well commercially but it was well received critically and the album was meant to start the foundation for all other Terror Squad members to release their solo projects.^{[citation needed]}

Big Pun also contributed vocals to the song Piña Colada with rapper Sheek Louch from the compilation album Ryde or Die Vol.1.